The crystals mainly consist of calcium hydroxyapatite Ca10(PO4)6(OH)2 and small percentages of carbonate and fluoride.
ĭentin is less hard than enamel but still harder than bone and is composed of weight 70% mineralized material, 20% organic material, and 10% water. The physical properties of the dentin-enamel junction (DEJ) have been examined, and the tensile cohesive strength of this structure is 51.5 MPa. A frequent marker of aging is cementicles, small round calcified bodies on the cementum or periodontal ligament. With aging, many cementocytes die, and the cementum loses its regenerative population of cells. The interface between dentin and enamel in the immature developing tooth is composed of enamel epithelium and dental mesenchyme. The enamel covers coronal dentin, while the radicular dentin is covered with cementum.Ĭementum is similar to bone in structure and composition, has cementocytes that occupy lacunae, and is composed of an inorganic substance and mineralized organic material. The latter is localized in the intercellular spaces of the dental papilla and follicle. Enamel has a small percentage of proteins: amelogenin, enamelin, and perlecan. The histological sections cannot examine its structure because the crystals dissolve during decalcification, a procedure that enables cutting the teeth when grossing the specimen. Mature enamel is organized in long thin rods of hydroxyapatite crystals. Enamel thickness is lower in the cervical region and thicker in masticatory surfaces (incisal ridge and cusps). The enamel on primary teeth has a whiter appearance being in an opaque crystalline form. Strong Retzius lines are formed during ameloblast traumas (such as the birth, which causes the creation of a "neonatal Retzius line") and are characterized by irregular structures of enamel crystals. In its mature state, enamel has an almost total absence of soft organic matrix. The lines of Retzius are the lines that appear in a histologic section of mature enamel, composed of bands of enamel rods. In the second phase of enamel maturation, ameloblasts form tight junctions and membrane infoldings from the apical ends of the cells, changing the pH from mildly acidic to near-physiologic, allowing the crystallization of the matrix. These crystals are organized in rod and interrod spaces away from the dentin. During development, the ameloblasts cover the entire surface of the developing tooth with an amorph matrix, rich in proteins, acellular, and avascular, that is then filled with ribbon-like crystals of carbonate-hydroxyapatite. Pulp is the inner part of the teeth and is composed of loose connective tissue produced by fibroblasts, many small vessels, and nerves. The teeth are anchored to the alveolar bone by the periodontal ligament, composed of fibrous tissue.Įnamel is produced by specialized epithelial cells, the ameloblasts. Dentin is produced by specialized cells called odontoblasts that align the matrix inside closely packed tubules those structures will undergo mineralization, giving structural resistance. The periphery of the dentin is composed of odontoblasts arranged in a picket fence fashion from the underlying pulp and have cellular processes extending into the dentin's tubules. This structure gives sensitivity to the dentin that produces pain when the protective layer of enamel is eroded. In response to physiologic or pathologic stimuli, odontoblasts can upregulate their protein synthetic activity. Enamel cannot regenerate and cannot be replaced. Mature enamel is acellular it is non-vital and not sensitive. The enamel is composed mainly of hydroxyapatite, an inorganic substance highly mineralized and aligned in rods to provide maximum protection to the underlying dentin. The crown is the part that emerges from the maxillary or jaw bone, has a hard and translucent surface (enamel) the root anchors the tooth to the alveolar bone and provides blood and nerve supply through the apical foramen.
The tooth can be divided into two main parts: the crown and the root. An indentation (cervical line) encircles the tooth marking a distinction between the crown and the root.
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